1. Field of the Invention
The present invention relates to an image reading apparatus. More particularly, the invention relates to an image reading apparatus including a sheet conveyance mechanism.
2. Description of the Related Art
Generally image reading apparatuses read images on sheets of documents by irradiating the sheets with light emitted from light sources such as light-emitting diodes (LED), and reading the sheets irradiated with the light with reading units such as cameras. The temperature in such image reading apparatuses tend to increase with the heat generated when their light sources and other electronic components are in operation. In recent years, many image reading apparatuses have been downsized. It is difficult, however, to radiate the heat generated in the downsized image reading apparatuses because it is difficult to provide them with heat radiating devices like fans. Therefore, some image reading apparatuses are designed to radiate the heat from their light sources without any additional heat radiating devices.
For example, such an image reading apparatus is proposed in Japanese Patent Application Laid-open No. 2008-147847. The Application relates to a linear light source apparatus and an image reading apparatus employing LEDs as light sources. According to the Application, two LEDs are mounted on two boards opposite to each other, so that the LEDs face each other. Between the two LEDs, a light guide member having ends close to the two boards is provided. Near the light guide member, a heat radiating member is provided, which extends along the light guide member, and has ends supported by the two boards. Consequently, a sheet of a document is irradiated with light emitted from the LEDs and incident via the light guide member when the LEDs are turned on. Heat generated when the LEDs are on is transferred to the heat radiating member to be radiated by the heat radiating member. Therefore, with this simple structure, it is possible to radiate the heat generated at the LEDs serving as the light sources to some extent without any additional heat radiating device.
However, when the heat generated at the light sources are transferred to the heat radiating member, the heat radiated by the heat radiating member raises the temperature of the air around the heating radiating member. Once this temperature increases, the temperature difference between the heat radiating member and the air becomes small. Consequently, it becomes difficult for the heat generated at the LEDs to effectively radiate through the heat radiating member.